1. Field of the Invention
The present invention relates to optical plates, and particularly, to an optical plate used in a backlight module.
2. Discussion of the Related Art
In a liquid crystal display device, liquid crystal is a substance that does not illuminate light by itself. Instead, the liquid crystal relies on light received from a light source to display information. In a typical liquid crystal display device, a backlight module powered by electricity supplies the needed light.
FIG. 12 represents a typical direct type backlight module 100. The backlight module 100 includes a housing 11, a light reflective plate 12, a light diffusion plate 13, a prism sheet 14, and a plurality of light emitting diodes 15 (hereinafter called LEDs). The housing 11 includes a rectangular base 111 and four sidewalls 113 extending around a periphery of the base 111. The base 111 and the four sidewalls 113 cooperatively define a chamber 115. Each LED 15 includes a base portion 153 and a light-emitting portion 151 disposed on the base portion 153. The LEDs 15 are electrically connected to a printed circuit board 16 that is fixed to the base 111 of the housing 11. The light reflective plate 12 is disposed on the LEDs 15 in the chamber 115. The light reflective plate 12 defines a plurality of through holes 122 that allows the light-emitting portions 151 of the LEDs 15 to pass through correspondingly. The light diffusion plate 13 and the prism sheet 14 are stacked in that order on the chamber 115. Light emitted from the LEDs 15 is substantially reflected by the light reflective sheet 12, and then enters the light diffusion plate 13. The light is diffused uniformly in the light diffusion plate 13, and finally concentrated at the prism sheet 14.
Generally, a plurality of dark areas may occur because of reducing intensity of light between adjacent LEDs 15. In the backlight module 100, each LED 15 further includes a reflective sheet 17 disposed on the top of the light-emitting portion 151, configured for decreasing the brightness of a portion of the backlight module 100 above the LED 15. However, the brightness of the backlight module 100 is still not uniform. One method of enhancing the uniformity of brightness of the backlight module 100 is to increase the space between the light diffusion plate 13 and the LEDs 15. However, increasing the space between the diffusion plate 13 and the LEDs 15 will also increase the thickness of the backlight module and further the overall intensity of the output light rays is reduced.
What is needed, therefore, is a new optical plate and a backlight module using the optical plate that can overcome the above-mentioned shortcomings.